The invention pertains generally to flight stabilizers and particularly to flight stabilizers for towed objects.
Objects towed from aircraft frequently have a drag component attached to it in order to stabilize the flight of the object and to assist in the extension of the object from the plane. The drag stabilizer is often referred to as drogue, cup, skirt or sock. It operates by increasing the amount drag being exerted on the connecting cable, thereby assisting the extension of the object, and by creating a partial vacuum behind the object, thereby minimizing oscillations and movements of the object in the air stream.
Certain design principles have been developed. The drag stabilizer generally has a frontal cross section smaller than the back cross section in order to prevent excessive drag. One common shape is a right frustocone, such as the drogue in U.S. Pat. No. 3,310,257 by E. N. Price, or the magnetic anomally detector (MAD) skirt in U.S. Pat. No. 3,204,890. Another shape frequently used is a bell, such as the cup in U.S Pat. No. 2,287,257 by W. P. Lear, or the drogue in U.S. Pat. No. 3,251,565 by M. C. Haist.
For larger towed objects, the drag component experiences instabilities arising from laminar flow along its surface and turbulent air effects behind it. Longitudinal holes are made through the drag component in order to eliminate or reduce the instabilities. Examples are found in U.S. Pat. Nos. 3,204,890 and 3,310,257.
The presently used drag skirt, or stabilizer, for a magnetic anomally detector (MAD) is a partially hollow right frustocone made from fiberglass and is attached to the detector by nonmagnetic beryllium copper screws in an arrangement similar to that shown in U.S. Pat. No. 3,204,890. This drag skirt has proven to be extremely expensive for several reasons.
The drag skirt is often cracked and ruined during landing, maintenance and flight. Approximately 50 skirts have to be replaced each year. Vibrations and shocks cause the relatively soft attaching screws to loosen or fail, causing the detector to fall in the sea. Impact on the water cracks or breaks the skirt and the entire detector assembly sinks. Approximately 30 detector assemblies are lost each year. The cost of the skirt is high because of the cost of the materials, the number of manufacturing operations, and the long manufacturing time.